Fungi cause a wide spectrum of disease states. The most common examples are relatively minor, localized infections of the skin and mucous membranes such as athlete's foot, vaginal yeast infections, and infections of keratinized nails. However, an ominously increasing number of fungi cause systemic disease with the involvement of internal organs. These have become serious and life-threatening problems that are very difficult to diagnose and even more challenging to treat in patients with impaired host-defense mechanisms. Part of the difficulty in treating fungal infections, especially in immunocompromised hosts, is the limited armamentarium of antifungal drugs. Currently-available drugs include polyenes (e.g., amphotericin B) that complex with fungal-membrane ergosterol, a number of azoles and allylamines that inhibit steps in the ergosterol biosynthetic pathway, flucytosine that inhibits nucleic acid synthesis, and Cancidas(r), a beta (1,3)- glucan synthase inhibitor. Unfortunately, amphotericin B has a number of acute and chronic adverse effects. Flucytosine has a narrow spectrum of activity and is plagued with treatment failures due to the development of resistant fungi. Azoles are only fungistatic and resistance to commonly used azoles is becoming a significant clinical problem. There is general agreement that there is a critical and immediate need for new antifungals with mechanisms of action different from current drugs. Our long-term goal is to discover novel antifungals that are active in the synthesis of an essential cell wall polymer, namely, beta (1,6) glucan. The synthesis of beta (1,6)glucan, which is absent in humans, is essential for fungal growth and represents an unexploited pathway for the development of antifungal drugs. We will accomplish this in three Specific Aims: One: Screen 5,000 compounds for beta (1,6)-glucan synthesis inhibitors using an established and validated in vitro assay. Two: Test compounds identified in Aim One for activity against a number of human fungal pathogens and to confirm that each compound inhibits beta (1,6)- lucan synthesis. Three: Test compounds for mammalian cell toxicity and for efficacy in an in vivo model of Candida albicans infection. Ultimately, this work will lead to the isolation of new classes of compounds for treatment of human fungal disease. We predict that, since humans do not have the pathway for beta (1,6) glucan synthesis, inhibitors will be safe and effective therapeutics.